Ultra sound probes are known. Specifically, such ultra sound probes have been used in the past to inspect right circular cylinders. In order to understand such inspection, first the parameters of a general inspection of an ordinary planar piece of material with acoustical transducers must be reviewed. Thereafter, the special problems in the examining a right circular cylinder will be set forth.
When a regular body (preferably a planar metallic body containing a weld) is examined, interrogation with five standard ultra sound transducers usually occurs. The ultra sound examination typically occurs from a planar surface on the suspect material disposed normally to a sound transducer. In understanding the direction of incidence of sound from interrogating transducers it is important to understand that in the acoustical interrogation here set forth, each transducer is both the transducer that sends interrogating and incident ultra sound as well as the receiver that receives the reflected ultra sound. It is the object of the ultra sound examination to provide inspection without destruction of the material--indicating either the physical limit of the material or the location of a possible defect. It will be understood, that the reflected signal received from the material being examined must be received in a direction that is parallel to the direction in which the signal was sent.
The ultra sound examinations here utilized occur in water. The preferred examination sites (the control rod drive housings and their supporting stub tubes) herein set forth are utilized with nuclear reactors which are typically flooded. Therefore, assuming that interrogation of the material being examined occurs at the above described angularities, problems of refraction in accordance with Snell's law occur.
Assuming that each transducer has its own interrogating direction, a standard array of transducers will include four transducers transmitting interrogating sound at 45.degree. angles within the material being non destructively examined. Thus, for the complete examination of a structure having a normal surface of incidence, transducers send and receive interrogating ultra sound at angles within the material being examined upwardly at 45.degree., downward at 45.degree., left at 45.degree., right at 45.degree., and finally normal to the incident surface of the material being non destructively examined.
The interrogating sound that is analyzed in the non destructive examination is that component of ultra sound reflected back along the path of sound incidence. This being the case, reflection must occur from at least one--and as many as three surfaces of a corner cube array within the material. It is to be understood that such reflection can occur within a number of structures within the material including finished dimensions of the material, cracks, metallic interfaces, slag deposits in welds, and the like.
It is not the purposes of this patent application to set forth the entire field of ultra sound including sophisticated problems of diffraction limited acoustical apertures and the art of interpretation of the received ultra sound results. This will be left to those having skill in the art. Rather, it is the purpose of this document to set forth the general problems encountered in producing an interrogating and receiving array of transducers in the examination of a right circular cylinder where the clearance at the point of material interrogation is extremely limited.
Further, where the surface being examined is a right circular cylinder, the angle of incidence of the interrogating ultra sound rays must be constantly adjusted to account for the immediate curvature of the surface being examined and the interaction of diffraction in accordance with Snell's law. It is usually desirable to have the ultrasonic transducer aligned with respect to the right circular cylinder center line so that the ultra sound beam upon contact with the surface of incidence interrogates and returns to the receiving transducer with predictability. Where the sending and receiving paths are not carefully controlled, results of interrogation cannot be received.
In normal examinations of right circular cylinders, all five transducers are normally disposed in a vertical string and vertically stacked overlying one another. The interrogating transducers are given angularities of examination with respect to the string in accordance with the parameters set forth above. Thereafter, the vertical string is moved upwardly and downward along any radius of the right circular cylinder until a complete examination of the surface to be interrogated has occurred. It is important to note, that where such transducers are vertically stacked, alignment of the probes with respect to the centerline of the cylinder being examined can occur; the predictability of the sound path for interrogation and receipt of the interrogating radiation is readily ascertainable from the point of incidence on the cylinder parallel to center line of the cylinder being interrogated.
Unfortunately, in examination and repair of right circular structures such as control rod drive housings and the so-called stub tubes to which such housing are fastened, overhead clearance can be impaired. This is especially true where the control rod drive housing and its supporting stub tube are being repaired or replaced within a flooded nuclear reactor.
When use of the vertical string of transducers is not permitted, the design of the probe to have the requisite angles of incidence to the surface of the right circular cylinder become other than trivial. This angle includes the interaction of Snell's law with both the orientation to, separation from, and offset of the interrogating transducer with respect to the particular curvature of the cylindrical surface being interrogated.
Accordingly, it is the purpose of this invention to set forth an especially designed ultra sound transducers which can rapidly and efficiently interrogate a right circular cylinder at a point of required non destructive inspection having limited vertical overhead clearance.